> ## Documentation Index
> Fetch the complete documentation index at: https://kleros.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# ERC-1497: Evidence Standard

> The V1 evidence standard defining how arbitrable contracts share MetaEvidence and Evidence with Kleros arbitrators via IPFS and event logs.

<Note>
  ERC-1497 is the V1 evidence standard. Kleros V2 replaces MetaEvidence with **Dispute Templates** registered in the `DisputeTemplateRegistry`, and extends evidence to support cross-chain submission. See the [Architecture guide](/developers/architecture) for V2 details.
</Note>

## Overview

ERC-1497 standardizes how DApps share context and evidence during dispute resolution. It defines two categories of information:

* **MetaEvidence**: The context of a dispute: the agreement, parties involved, ruling options, and the question jurors need to answer. Each dispute has one piece of MetaEvidence, created at the same time as the agreement.
* **Evidence**: Proof submitted by any party to support their position in a dispute.

Both are stored off-chain (typically on IPFS) and referenced on-chain through event logs.

***

## Interface

ERC-1497 introduces three events:

```solidity theme={null}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "../IArbitrator.sol";

interface IEvidence {
    /// @dev Emitted when meta-evidence is submitted.
    /// @param _metaEvidenceID Unique identifier of meta-evidence.
    /// @param _evidence IPFS path to metaevidence JSON.
    event MetaEvidence(
        uint256 indexed _metaEvidenceID,
        string _evidence
    );

    /// @dev Emitted when evidence is submitted.
    /// @param _arbitrator The arbitrator for the dispute.
    /// @param _evidenceGroupID Unique identifier of the evidence group
    ///        (typically the dispute ID or external ID).
    /// @param _party The address submitting the evidence.
    /// @param _evidence IPFS path to evidence JSON.
    event Evidence(
        IArbitrator indexed _arbitrator,
        uint256 indexed _evidenceGroupID,
        address indexed _party,
        string _evidence
    );

    /// @dev Emitted when a dispute is created to link meta-evidence
    ///      and evidence group to the dispute.
    /// @param _arbitrator The arbitrator for the dispute.
    /// @param _disputeID ID of the dispute in the Arbitrator contract.
    /// @param _metaEvidenceID ID to look up the MetaEvidence event.
    /// @param _evidenceGroupID ID for the evidence group.
    event Dispute(
        IArbitrator indexed _arbitrator,
        uint256 indexed _disputeID,
        uint256 _metaEvidenceID,
        uint256 _evidenceGroupID
    );
}
```

***

## MetaEvidence JSON

MetaEvidence is a JSON file hosted on IPFS that provides dispute context:

```json theme={null}
{
  "category": "Escrow",
  "title": "Payment for website development",
  "description": "Alice hired Bob to develop an e-commerce website...",
  "question": "Should the payment be released to the developer?",
  "rulingOptions": {
    "type": "single-select",
    "titles": ["Refund Buyer", "Pay Developer"],
    "descriptions": [
      "Return the funds to the buyer",
      "Release the funds to the developer"
    ]
  },
  "fileURI": "/ipfs/QmContractTerms...",
  "fileHash": "0x...",
  "evidenceDisplayInterfaceURI": "/ipfs/QmEvidenceDisplay..."
}
```

| Field                         | Description                                        |
| ----------------------------- | -------------------------------------------------- |
| `title`                       | Short title for the dispute                        |
| `description`                 | Detailed context for jurors                        |
| `question`                    | The question jurors must answer                    |
| `rulingOptions`               | Labels and descriptions for each ruling choice     |
| `fileURI`                     | IPFS path to the agreement or contract document    |
| `fileHash`                    | Hash of the linked file for integrity verification |
| `evidenceDisplayInterfaceURI` | Optional custom UI for displaying evidence         |

***

## Evidence JSON

Each piece of evidence is a JSON file:

```json theme={null}
{
  "name": "Delivery confirmation email",
  "description": "Email from the developer confirming delivery of the website",
  "fileURI": "/ipfs/QmEvidence...",
  "fileHash": "0x...",
  "fileTypeExtension": "pdf"
}
```

***

## Integrity Verification

The JSON for both MetaEvidence and Evidence contains `fileHash` fields. Arbitrators use these hashes to verify that files have not been tampered with after submission. IPFS content-addressing provides built-in integrity for files hosted on IPFS, since the CID itself is derived from the file content.

***

## Usage in a V1 Contract

```solidity theme={null}
contract SimpleEscrowWithERC1497 is IArbitrable, IEvidence {
    // Emit MetaEvidence at contract creation
    constructor(string memory _metaEvidence) {
        emit MetaEvidence(0, _metaEvidence);
    }

    // When creating a dispute, link it to the meta-evidence
    function raiseDispute() external payable {
        uint256 disputeID = arbitrator.createDispute{value: msg.value}(
            numberOfChoices, extraData
        );
        emit Dispute(arbitrator, disputeID, 0, 0);
    }

    // Allow parties to submit evidence
    function submitEvidence(string calldata _evidence) external {
        emit Evidence(arbitrator, 0, msg.sender, _evidence);
    }
}
```

***

## V2 Replacement

In V2, ERC-1497 is replaced by:

* **Dispute Templates**: Registered in `DisputeTemplateRegistry` with Mustache-style variable interpolation. Templates define the dispute question, ruling options, and policy reference.
* **`DisputeRequest` event**: Replaces the `Dispute` event, linking disputes to templates by `templateId`.
* **Cross-chain evidence**: Evidence can be submitted on either the home or foreign chain, with the Court UI consolidating from both.

***

## References

* [ERC-1497 on GitHub](https://github.com/ethereum/EIPs/issues/1497)
* [Reference implementation](https://github.com/kleros/erc-792/blob/master/contracts/erc-1497/IEvidence.sol)
* [Archon library](https://github.com/kleros/archon)  JavaScript library for fetching and validating evidence